Two radioactive materials \[{{X}_{1}}\] and \[{{X}_{2}}\] have decay constants \[10\lambda \] and \[\lambda \] respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of \[{{X}_{1}}\] to that of \[{{X}_{2}}\] will be \[1/e\] after a time [IIT-JEE (Screening) 2000]

• A.            \[1/(10\lambda )\]            
• B.            \[1/(11\lambda )\]
• C.            \[11/(10\lambda )\]
• D.            \[1/(9\lambda )\]